The present invention relates to an apparatus and a method for recording and reproducing a data stream including an image and sound, and a recording medium for the same.
In recent years, CS digital broadcastings utilizing the MPEG2 system format, including an efficiency-enhanced encoding system for moving images, has come into practice.
In the MPEG2 system, encoded image, sound, and like data are called elementary stream. The elementary stream is transmitted in a form named PES (Packetized Elementary Stream) packet. The PES packet has a structure composed of a PES header followed by a PES payload constituting a data portion.
The foregoing CS digital broadcasting utilizes a multiplex system called transport stream. In a transport stream, image, sound, and like data are transmitted by dividing and multiplexing them into a transmission unit called a transport packet having a fixed length of 188 bytes.
When recording and reproducing a data stream, which is encoded with the MPEG2 system on a magnetic tape by using a digital video tape recorder (VTR), during normal playback operation the original image is accurately reproducible, since the recorded packets are reproduced in the sequential order of the recording. In the case of high-speed playback operation, such as a high-speed search, the image can not be reproduced accurately because the packets are reproduced intermittently since a magnetic head traces only a portion of each of a plurality of recording tracks, as the head traces the tracks transversely.
For this reason, a technique has been devised in that an image is recorded in predetermined, discontinuous locations (rectangular areas shown by hatch lines in FIG. 6) on a plurality of tracks on a recording medium. The reproduction heads are traceable during a high-speed playback operation so that the image is reproduced by using the data, for example, as shown in FIG. 6. The rectangular areas shown by hatch lines in FIG. 6 indicate the recording tracks and arrows indicate the paths of the reproduction heads during the high-speed playback operation. FIG. 6 also shows that the image can be reproduced if a head xe2x80x9cAxe2x80x9d, among the two reproduction heads, traces a path 61 and a head xe2x80x9cBxe2x80x9d traces a path 65.
One example of the above-described digital VTR of the prior art will now be described hereinafter by referring to the drawings.
FIG. 5 depicts a diagram of a control block of the digital VTR of the prior art. The control block in FIG. 5 includes: (a) a rotary cylinder 103 (hereinafter referred to as cylinder), of which the outer periphery is provided with a plurality of magnetic recording/reproduction heads for recording and reproducing a signal, and wound for approximately 180xc2x0 on the cylinder is magnetic tape 104; (b) a cylinder driving circuit 114 for driving and controlling the rotation of the cylinder 103; (c) a reproduction process circuit 112 for executing signal processing such as equalization, error correctional decoding, etc. of the signal reproduced by the magnetic recording/reproduction heads on the cylinder 103; (d) a SB number/track number detection circuit 115 for detecting numbers of a reproduction sync block and a recording track decoded by the reproduction process circuit 112; (e) a HSW signal generation circuit 105 for producing a rotational phase signal (hereinafter referred to as HSW) for the cylinder based on a rotational position signal and a rotation detecting signal of the cylinder 103; (f) a CTL head 107 for recording and reproducing a control signal (hereinafter referred to as CTL signal) on and from the magnetic tape 104; (g) a CTL signal detection circuit 108 for detecting an edge of the reproduced CTL signal; (h) a phase difference detection circuit 109 for detecting a difference in phase of the two signals input to it; and (i) a tape driving circuit 110 for executing a driving control of a capstan motor 111, which controls a travelling speed of the magnetic tape 104 based on a phasing error input from the phase difference detection circuit 109. The phase difference detection circuit 109 is also input with signals from three circuits, i.e. the SB number/track number detection circuit 115, the HSW signal generation circuit 105 and the CTL signal detection circuit 108.
The conventional digital VTR constructed as above operates in a manner, which will be described hereinafter.
A control operation in the ordinary playback mode is as follows.
The cylinder 103 rotates at a constant speed according to a control output of the cylinder driving circuit 114. The rotation causes the HSW signal generation circuit 105 to output a HSW signal. The CTL head 107 reproduces a CTL signal recorded in the magnetic tape 104 and a leading edge of the CTL signal is detected by the CTL signal detection circuit 108. The phase difference detection circuit 109 detects a difference in phase between the HSW signal and the leading edge of the CTL signal input to it.
The detected difference in phase is output as an error signal and it is supplied to the tape driving circuit 110, which in turn controls a traveling speed and a phase of the magnetic tape 104 with the capstan motor 111.
The phase control between the HSW signal and the CTL signal is thus executed by the foregoing series of feedback controls so as to maintain the reproduction heads to accurately trace the recording tracks on the magnetic tape.
A control operation in a high-speed playback mode will now be described as follows.
FIG. 6 depicts a tape pattern for the high-speed playback mode, in that arrows with dotted lines indicate the directions and locations where the magnetic heads scan through high-speed playback fields (rectangular areas shown by hatch lines) located discontinuously over a plurality of helical tracks 101, when the tape speed is octupled. Reference characters 0a through 7b in FIG. 6 identify track numbers and the xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d suffixed to the track numbers indicate corresponding azimuths of the magnetic heads during recording. In the case of the two-head azimuth system of this example, the two magnetic heads xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d record or reproduce alternately on and from the tracks and angles (azimuths) of magnetizing direction in recording and reproduction by the two heads are altered in order to reduce interference of signals between the adjoining tracks. Therefore, the track xe2x80x9caxe2x80x9d recorded with the head xe2x80x9cAxe2x80x9d is reproducible with the head xe2x80x9cAxe2x80x9d but not reproducible with the head xe2x80x9cBxe2x80x9d. The same also applies to the track xe2x80x9cbxe2x80x9d recorded with the head xe2x80x9cBxe2x80x9d.
The cylinder 103 is controlled for a constant rotational speed by the cylinder driving circuit 114 based on a reference cycle (not shown in the figure) corresponding to the octuple speed of the tape. The reference cycle in this mode is nearly equal to a reference cycle for the ordinary speed or a reference cycle in the ordinary playback mode.
The magnetic tape 104 is driven by the capstan motor 111 at a speed octuple of the ordinary speed. Therefore, the CTL signal detection circuit 108 outputs a CTL signal divided by eight in order to generally equalize the cyclic period with the HSW signal, since a cycle of the reproduced CTL signal becomes one eighth of that of the ordinary playback speed.
Then, the phase difference detection circuit 109 detects a difference in phase of the CTL output signal with the HSW signal in the same manner as in the case of the ordinary playback. And, the tape driving circuit 110 performs a rotational phase control of the capstan motor 111 to automatically adjust a travelling phase of the magnetic tape 104.
Incidentally, there are eight different timings for the eight-part division, since the dividing timing for the CTL signal reproduced by the CTL signal detection circuit 108 is not specified. For this reason, a pull-in of phase may be completed while the heads are scanning through fields other than the high-speed playback fields (the areas shown by hatch lines in FIG. 6) at a rate of seven times out of eight trial operations. Referring to the head xe2x80x9cAxe2x80x9d, for example, a path 61 along an arrow with dotted line in FIG. 6 is a regular path for the high-speed playback and paths 62 through 68 are for irregular pull-ins of the phase. Parenthetically, rectangular areas shown by hatch lines along a path 65 are reproduction fields for the head xe2x80x9cBxe2x80x9d, but not for the head xe2x80x9cAxe2x80x9d.
A second feedback loop using the track numbers and the SB numbers is therefore adapted in order to avoid these conditions of irregular pull-in of the phase.
A control operation in the second feedback loop will be described hereinafter.
Upon completion of an ordinary pull-in operation of the phase, the SB number/track number detection circuit 115 detects a SB number and a track number that are block numbers of image data read by the heads during scanning at the moment. Location of the scanning at that moment is uniformly determined by the SB number and the track number. Therefore, if the heads scan along the positions shown by the paths 62 through 68, the detection circuit 115 detects a deviation in number of tracks from the proper scanning position. The detected amount of phase deviation is input to the phase difference detection circuit 109, so that a phase error corresponding to the deviated number of tracks is calculated as an offset, and it is added to the phase error.
As the result, a pull-in operation of the phase is started by the second feedback loop, and the head xe2x80x9cAxe2x80x9d begins to scan the path 61.
An optimum head scanning for the intended high-speed playback fields is thus achieved with the two-step control operation as described above.
When shifting from ordinary playback to high-speed playback operation, the HSW signal and a dividing signal of the CTL signal are phase-locked first. The heads are then phase-locked in the correct track paths by way of detecting the SB number and the track number reproduced from the helical scanning tracks and calculating an amount of deviation of the scanning paths of the heads. Consequently, an apparatus of the prior art for recording and reproducing a data stream has a problem that it takes considerable time for shifting into high-speed playback operation, therefore, it takes a long period of time to reproduce an image in the high-speed playback operation.
An apparatus of the present invention for recording and reproducing a data stream includes: (a) a recording process means for generating, from an input data stream, a recording packet for ordinary playback and a data stream for high-speed playback and for generating a composite recording packet by inserting a recording data block within the data stream for high-speed playback into a predetermined position in the recording packet for ordinary playback; (b) a control signal generation means for generating a control signal, which is superposed with an identification mark for identifying the high-speed playback data stream; (c) a rotary cylinder provided with a magnetic head for recording and reproducing the composite recording packet on and from a magnetic tape; (d) a fixed magnetic head for recording and reproducing the control signal superposed with the identification mark on and from the magnetic tape; and (e) a control signal detection means for detecting the identification mark recorded on the magnetic tape during a high-speed playback operation.
A method of the present invention for recording and reproducing a data stream includes the steps of: (a) generating a recording packet for ordinary playback and a data stream for high-speed playback from an input data stream (a data stream input to it); (b) generating a composite recording packet by inserting a recording data block within the data stream for high-speed playback into a predetermined position in the ordinary playback recording packet; (c) generating a control signal superposed with an identification mark for identifying the high-speed playback data stream; (d) recording and reproducing the composite recording packet on and from a magnetic tape; (e) recording and reproducing the control signal superposed with the identification mark on and from the magnetic tape; and (f) detecting the identification mark recorded on the magnetic tape during a high-speed playback operation.
A recording medium of the present invention is a medium that is recorded with a composite recording packet, which is generated through the steps of: (a) generating a recording packet for ordinary playback as well as a data stream for high-speed playback from an input data stream containing image data and sound data; and (b) inserting a recording data block within the high-speed playback data stream into a predetermined position in the ordinary playback recording packet at intervals of a predetermined unit of plural tracks, wherein the recording medium is further recorded in its control track with an identification mark for identifying a specific track in each unit of the plural tracks recorded with the data stream for high-speed playback, by superposing it upon a control pulse.
Also, the identification mark for identifying the specific track in each unit of plural tracks is recorded in the control track by superposing it on the control pulse, at the same time the data stream is recorded. The magnetic head thus travels along a predetermined path within each unit of plural tracks according to the reproduced identification mark and control pulse during a high-speed playback operation.
Accordingly, the structure as described above can start reproduction and output the data stream for high-speed playback within a short period of time.